The present invention relates to an apparatus for measuring the pressure of a fluid in a pressurizing chamber of a micromachine apparatus that transfers a liquid for industrial or consumer use.
In recent years, the size and weight of sensors and actuators have been significantly reduced, and there is a strong demand for a further reduction in the size and weight. Correspondingly, micromachining based on the etching of silicon wafers has been proposed and put into practical use, and this technique is being extensively researched and applied to ink-jet recording heads and blood sensors.
FIGS. 10(a)-10(c) show an operational principle of an ink-jet recording head, which is one example of such applications. FIG. 10(a) is a cross sectional view showing a stable condition prior to ink injection. FIG. 10(b) is a cross sectional view showing a condition in which ink is pressurized. FIG. 10(c) is a cross sectional view showing a condition in which ink droplets are formed.
Ink 17 is filled in an ink refilling section 13, a restraining channel 14, an ink pressurizing chamber 15 and a nozzle 16 that constitute an ink channel, and a piezoelectric element 11 is conductively fixed to a movable portion 12 of the ink pressurizing chamber 15. When a drive circuit (not shown) applies an electric signal to the piezoelectric element 11, the surface of the piezoelectric element 11 is reduced in size by an inverse piezoelectric effect to deform the piezoelectric element 11 together with the movable portion 12, as shown in FIG. 10(b), thereby pressurizing ink in the ink pressurizing chamber 15 to cause an ink column 18 to be ejected from the nozzle 16. The restraining channel 14 controls the flow of ink 17 to the ink refilling section 13 to efficiently flow to the nozzle 16. When the level of the electric signal to the piezoelectric element 11 is reduced to start returning the deformed piezoelectric element 11 to its original form, the tip of the ink column 18 is broken and ejected in the same manner as ink droplets 19, while the remaining part of the ink column 18 flows back into the nozzle 16. This condition is shown in FIG. 10(c). When the electric signal is subsequently lost, the piezoelectric element returns to its original shape and ink 17 returns to the stable condition, so that the initial condition shown in FIG. 10(a) is established.
Recent advancement in electronic technology has contributed to the improvement of techniques in which a central processing device is built in an apparatus that includes multiple nozzles for the precise printing of characters, or that uses color inks to record full-color images. FIG. 11 shows an example of such an ink-jet recording head, wherein FIG. 11(a) is an exploded perspective view and FIG. 11(b) is a cross sectional view.
In this example, seven components of the ink channels shown in FIG. 10 are integrated together to form a head body 10. The piezoelectric elements 11 are conductively fixed to portions of the channels corresponding to the ink pressurizing chambers. Each connection portion 22 of a flexible wiring board 20 having a copper foil pattern 21 is connected to each piezoelectric element 11 with solder 22. The head body 10 is positioned in a guide hole 31, and housed and fixed in a case 30. A nozzle section is formed in a portion of the body that is inserted into the guide hole 31 to eject ink downwardly. In this manner, an ink-jet recording head 1 is constituted as a single unit.
In developing a micromachine apparatus such as the ink-jet recording head 1 for transferring a fluid, it is very important to measure the pressure generated inside a pressurizing chamber 15 to evaluate the resistance of the fluid. FIG. 12 is a cross sectional view of the integral part of the apparatus showing an example in which a generally known small pressure sensor 2 is incorporated into a micromachine apparatus for such a purpose. In this figure, the pressure sensor 2 is disposed to communicate with the ink pressurizing chamber 15. As the pressure sensor 2 that is often used for such applications, for example, PYS-3-50H manufactured by Toyoda Machine Works, Ltd. is well known. This sensor, however, is approximately .phi.3 mm in size and is too large in relation to the size of the ink pressurizing chamber 15 of the micromachine apparatus, for example, 0.5 mm (W).times.3 mm (L).times.0.1 mm (D), so that changes in the volume of the pressure sensor 2 affect extremely to prevent an accurate pressure value from being obtained.
Another known pressure measurement method is described in, "Dynamic Analysis of the Ink Speed in Kyser Ink Jet" (Prof. Kiyohiro of Yamanashi University) in the 1987 Printing Society Journal. This method is shown in FIGS. 13(a) and 13(b). In these figures, a pressure detection chamber 15b is additionally provided in the ink pressurizing chamber 15, and a piezoelectric element 11b for detection is provided on the side wall of the chamber 15b to measure the pressure. This method requires the inclusion of the pressure detection chamber 15b, hampering the miniaturization of the apparatus and requiring a measurement apparatus different from the actual micromachine apparatus to be produced.
It is an object of this invention to provide an apparatus for inexpensively measuring the pressure in the pressurizing chamber of a micromachine apparatus in its actual-use condition or a similar condition, without large changes in volume or the provision of a special detection chamber constructed based on the existing technology.